1. Field of the Invention
The present invention relates generally to germicidal lamps, and more particularly the invention relates to such devices used in air and surface sterilization.
2. Description of Related Art
One industry that is mature and economically sensitive to costs is the heating, ventilation and air conditioning (HVAC) industry. Because of the competitive nature of both the construction and HVAC industries, HVAC systems must be inexpensive to purchase and install. Of a more global interest though, is the cost to operate and maintain HVAC systems. Often, a building owner will replace an aging HVAC system as the reduction in operating and maintenance costs can offset the retrofit cost, sometimes in a matter of months.
Broad social and energy policies also favor efficient HVAC systems. In these days of electricity conservation and deregulation, it has become even more important to conserve energy consumption. Recently, entire electrical grids have shut down on very hot days in part because of the huge electrical demand from inefficient HVAC systems running at extreme capacity. Furthermore, energy conservation translates directly into improved environmental conditions and decreased reliance upon foreign petroleum.
HVAC systems are typically comprised of a cooling and heating section for, respectively, cooling and heating the air. An HVAC system will also include fans and ductwork for moving this conditioned air where it is needed. In most HVAC systems, air is drawn in, filtered, cooled and dehumidified or heated and humidified, and then delivered to a space. The greatest portion of this air is drawn from the space for recirculation through the HVAC system.
One factor impacting design and operation of HVAC systems is indoor air quality (IAQ). A major consideration in IAQ today is the amount of outdoor air introduced by an HVAC system into an otherwise sealed space. The HVAC industry and others have adopted standards for the introduction of outdoor air into spaces serviced by an otherwise closed HVAC system. These include offices, residential, commercial, industrial and institutional spaces, and modes of transportation such as cars, buses, planes and ships. In addition to controlling indoor air for occupant comfort, the goal of most HVAC systems is to provide air with reduced levels of particulate, gases and bioaerosols, be it for semiconductor, pharmaceutical or food processing facilities, hospitals, schools or offices and now the home.
Various reasons have contributed to the lack of success in utilizing germicidal lamps for bioaerosol control (IAQ), except for limited and specialized purposes. The functional implementation of such devices in air moving systems has been limited generally to expensive portable units with questionable efficacy. However, non-moving air devices can be found as wall or ceiling mount systems where the germicidal lamp is situated in a minimum air movement, and proper ambient air temperature area. A typical germicidal tube is designed to operate in still air at 80-90° F. Germicidal lamps have sensitive physical characteristics, including their plasma gases, mercury and the partial pressures thereof.
When a conventional germicidal lamp is used to irradiate moving airstreams, the air moving across the tube removes heat and lowers the tube's temperature. The tube's mercury then condenses such that the emission of the germicidal wavelength of 253.7 mm decreases. This decrease can be up to 75% when the tube wall temperature reaches 58° F. Also, at lower internal temperatures, tube components degrade quicker, shortening tube life. This phenomenon, known as skin effect cooling, requires a notable increase in the number of conventional tubes required for a given level of performance. Increasing the number of tubes reduces the available square or open area for airflow. This in turn requires the airs' velocity to increase, which decreases the dose (time times intensity) and air volume. If such a system could be made to work, it would require an increase in fan horsepower, light energy and in the number of expensive tube replacements.
Conventional germicidal lamps emit ultraviolet light at both the primary and secondary emission lines of mercury (254 nm and 187 nm). At mercury's 187-nm line, ozone is created and in many applications of germicidal lamps, such as in water, ozone is desirable. However, ozone has strict threshold limit values in air due to its strong oxidative properties and potential harm to humans. Although numerous companies have attempted to apply germicidal lamps to HVAC systems, standard germicidal lamps have proved unsatisfactory. Typically, a conventional germicidal lamp performs best when installed in a system or room where the air is still and/or warm. Despite the clear benefits of germicidal lamps, problems such as decreased output in moving and/or low temperature air, reduced air changes and ozone production have prevented their use in all but specialized environments.
Germicidal fixtures continue to enter the HVAC market. Recent entries have been sold under the Germ-O-Ray and Germitroll trademarks. The particular capabilities and design of these devices is not known to the inventors, though it is believed both devices use conventional tubes that will suffer from the criteria outlined above when installed in air ducts.
For further information concerning improvements in electric discharge devices, which are directed to overcoming such problems, reference is made to the above-identified patent applications. These other patent applications describe excellent devices and methods for using germicidal lamps to make HVAC systems more efficient, less costly to operate and maintain, and to provide better IAQ for a healthier environment.
Germicidal tubes differ significantly from electric discharge devices used in ultraviolet gas spectroscopy (VUV tubes). Germicidal tubes are low-pressure types that emit UV light at the primary and secondary emission lines of mercury—254 nm and 187 nm. In contrast, VUV tubes are high-pressure types that operate at high temperatures and as a consequence, emit different spectral lines and intensities.
Besides IAQ standards that include HVAC systems, there are numerous other standards that apply to HVAC systems, their design, construction and components. One set of standards that applies to HVAC (and other) electrical equipment has been promulgated by the National Electrical Manufacturers Association (NEMA). NEMA has published standards regarding enclosures for electrical equipment including HVAC equipment installed outdoors. A NEMA Type 4 enclosure is constructed for outdoor use and provides a degree of protection against rain, sleet, snow and the formation of ice. A NEMA Type 4 enclosure also provides a degree of protection against windblown dust, dirt, splashing water, hose-directed water and corrosion. A NEMA Type 4 enclosure should protect personnel against incidental contact with the enclosed equipment. Additional information is available from the NEMA Web site at www.nema.org.
One common use of germicidal lamps is in water treatment where ozone is generally considered desirable. However, the ozone in these water treatment systems is controlled and not released to the atmosphere. Furthermore, their ultraviolet tubes are enclosed in a quartz sleeve to create an insulating, dead air space, thereby elevating the tubes' ambient operating temperature. This is necessary because the water would otherwise draw heat away from the tube in the same manner as air or as in skin effect cooling.
Germicidal lamps for water treatment must have some amount of protection from the water itself. In particular, these lamps are sleeved and further isolated in some manner to be water tight against and compared to the water vessel in which the tube is installed. However, water application fixtures have not been considered or used in air treatment systems. Also, water application fixtures have not been produced for HVAC use or for air treatment use in outdoor applications.